Electric signal pick-off device



Aug. 10, 1954 w. LEATHERS 2,686,235

ELECTRIC SIGNAL PICK-OFF DEVICE Filed Feb. 27, 1955 41 r: 29 FIG! 39 FIG.2

INVEN TOR.

WARD LEATHERS ATTORNEY Patented Aug. 10, 1954 UNITED STATES PATENT OFFICE ELECTRIC SIGNAL PICK-OFF DEVECE Ward Leathers, Brooklyn, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application February 27, 1953, Serial No. 339,497

Claims. 1

This invention is concerned with a pick-off device and more specifically with an electric circuit making and breaking device for a pair of circuits, of the type employed as a control element in a hydraulic servo system such as that disclosed in a copending application, Serial No. 284,606 filed April 26, 1952.

The object of this invention is to provide an improved sliding contactor which employs a parallel sliding movement along the surface of the contact drum, this parallel movement being par allel to the rotation axis of the contact drum so that the errors or non-linearity of the signals, obtained from the previous type of pick-off will be eliminated.

Another object of this invention is to provide an improved. configuration for the insulation strip which divides the contact drum into separate contact areas. The improved configuration thus contemplated allows a great reduction in speed of revolving the contact drum and therefore greatly reduces the amount of Wear which takes place at the sliding contact. To these and other ends, one embodiment of the invention is illustrated in the drawings, in which:

Fig. 1 is a plan view of the pick-off Fig. 2 is a cross-section view of the contactor and drum taken along the line 2-2 of Fig. 1;

Fig. 3 is a detail plan view showing the relative position of the parts when the contactor is displaced to one side of its neutral position illustrated in Fig. l

Fig. 4 is a detail view of the surface of the drum unrolled showing the configuration of the insulating strip and Fig. 5 is a plan view of a previous type of pick-01f illustrating the path of its contactor over the drum.

A pick-off, as the term is being used in this disclosure, is adevice for producing error signals in a servo system. The servo system will be energized when error signals other than zero are present, and the energized servo system will produce movement of controlled elements and at the same time will produce a reduction of the error signal toward zero. This same pick-ofi might be used merely as a control element, in a system which does not have any follow-up element for reducing the energizing signal to zero, but which system merely uses the amount of signal to determine the amount of energization of the system.

Other uses may be found for this pick-ofi unit which is basically an electric switching device having a common contactor which makes alternate contact with two separate conducting surfaces. on a rotating drum. The common contactor is supported from a pivoted arm for movement over the surface of the drum. At a neutral position the contactor makes contact for equal periods of time with each of the conducting surfaces alternately; while on either side of neutral the contactor will increase the periods of contact with one of the conducting surfaces, and correspondingly decrease the periods of contact with the other surface. When-the device is being used in a servo system, such as that disclosed in the aforementioned copending application, Serial No. 284,696, the neutral position corresponds to zero error,

In Fig. l, the whole pick-cit unit is illustrated and it will be observed that the unit consists of a contact drum ii which has a surface composed of some metallic material which is a good electrical conductor, such as copper. This contact drum ii is carried for rotation by a pair of bearing members l3 and may be continuously rotated by means of a gear l5 which is secured to one end of the shaft for the drum H by means of a pin 1?. The surface of contact drum II is divided into two separate areas I9 and 2|, which are separated by a strip of insulating material 23. Each of the surface areas 59 and 2| may be electrically connected to a separate circuit by any convenient means (not shown) such as contact brushes or the like. Under the surface of the drum ii, there is a layer of insulating material 25 (see Fig. 2) in Order to insulate the surface areas !9 and 2! from the supporting structure, including bearing members l3. This layer 26 may be the same material as insulating strip 23 if desired, or any other suitable insulating material.

Electrical contact with each of these surface areas [Sand 2! is made alternately as the drum H is rotated by means of a contactor 25 which may be made of any convenient electric brush material depending upon the current rating and related considerations. The contactor 25 is supported by a bracket 21 which is fastened to a short cross arm 2% by means of a corresponding pair of brackets 3i and a pin 33. The cross arm 29 pivoted to the end of a pick-on arm 35 by means of an upstanding pin 3?. The contactor 25 is kept pressed against the surface of drum. H by means of a coil spring 39 which is held in place by means of two lugs 4i and i3. Lug 4! is located on the cross arm 29 behind the brackets 3! which support the contactor 25, while lug 43 is located on the face of an angle bracket amiss 45 which in turn is fastened onto the upper surface of the arm 35 by means of rivets as illustrated. There is a turned-up stop member 41 which is located near the end of pick-off arm 35 and which acts to limit the movement of cross arm 29 so that when the pick-off unit is being assembled or disassembled the coil spring 39 will not tend to fall away from its lugs 4| and 33.

It will be noted that the pick-off arm 35 is pivoted about an axis which lies at right angles to the longitudinal axis of the drum ll. Furthermore, the location of the arm 35 along its pivot axis relative to the drum H (see Fig. 2) is such that the center of the contactor 25 touches the surface of drum II on a line which lies in a horizontal plane passed through the longitudinal axis of drum By this means, when pick-01f arm 35 is pivoted to one side or the other of the neutral position illustrated in Fig. 1, contactor 25 will slide back and forth on a line which is parallel to the longitudinal axis of drum ll. This movement of contactor 25 is in distinction to the movement which would take place for a contactor of the old style pick-off such as that illustrated in Fig. 5. It will be noted that the contactor of the old style pick-off will follow an arcuate path on the surface of its drum such as that illustrated by a dashed line 49 (Fig. 5) It is pointed out that such arcuate travel of the contactor over the surface of the drum will produce non-linear changes in the signal produced by the pick-off as its arm pivots relative to the drum. The construction embodied in my invention eliminates this source of non-linear response of a system which employs this type of pick-off contact. It is this parallel sliding motion of contactor 25 which produces a linear signal effect when the contactor is moved from its neutral position in either direction as illustrated in Fig. 1.

Fig. 3 illustrates the swivel action of the mounting for contactor 25 which allows the contactor to maintain an even pressure over its entire width, which is in contact with the surface of drum i. It will be noted that the width of contactor 25 is in this instance equal to the width of the insulating strip 23 as measured parallel to the longitudinal axis of the drum I. If desired, the width of contactor 25 might be greater or less than that of the strip 23. Any such difference in width of contactor 25 will of course produce either an overlap in the alternate contacting of surface areas l9 and 2| on the contactor drum H,

or a time lag between the alternate contacting. That is, if contactor 25 is wider than strip 23, then when the contactor 25 is in its neutral position and the drum II is rotating, the periods of alternate contacting of areas l9 and 2| will overlap such that both areas l9 and 2| will be contacted simultaneously for very short periods each cycle. On the other hand, if contactor 25 is narrower than strip 23, then, with contactor 25 at neutral, there will be short periods between the alternate contacting of areas i9 and 2| when neither area I9 nor 2| will be contacted. It will now be evident that the action of the pick-off unit is such that by maintaining a continuous rotation of drum II, the two circuits (not shown) connected to surface areas l9 and 2| will be alternately connected to contactor 25 and its supporting structure for producing an alternate energization of the two circuits. The time duration of alternate energizations in each cycle may be varied by pivoting the pick-off arm 35 in either 4 direction from its neutral position (illustrated in Fig. 1).

Fig. 4 illustrates the configuration of the insulating strip 23 which has a zig-zag shape when viewed (as illustrated in Fig. 4) by unrolling the surface of drum II. It will be observed that by means of this configuration, two complete cycles of alternate contacting of the two surface areas l9 and 2| may be had for each revolution of the drum II. In this way, the speed of revolving drum Il may be reduced one-half while the same frequency of alternate contacting of the two surface areas is maintained. For this reason, a greatly reduced brush travel speed of the contactor 25 over the surface of the drum M will be accomplished, and, consequently, much less wear of the contactor 25 and also of the surface of the drum II will take place. This means that undesirable grooving of the surface of drum U will be reduced to a minimum.

It will be clear that the configuration of strip 23 may be made with additional changes in direction or zig-zags, in order to increase the number of additional cycles per revolution of the drum H and thus further reduce the speed of travel of the surface of drum relative to the contractor 25 while maintaining the same frequency.

The details of a specific embodiment of the invention have been illustrated in accordance With the applicable statutes; but this is to be taken as illustrative only and in no way as limiting my invention.

I claim:

1. In an electrical pick-off device having a contact drum, the surface of which is divided into two separate areas being separated by an insulating strip with a predetermined shape, and a sliding contactor riding on the surface of said drum, said contactor being movable over the surface of said drum carried by an arm pivoted about a point fixed relative to the rotational axis of said drum, the improvement comprising swivel mounting means for said contactor to maintain even contact pressure over the entire contacting surface of the contactor, and means mounting said contactor for contact movement along the surface of said drum parallel to the rotational axis of the drum.

2. In an electrical pick-01f device having a contact drum, the surface of which is divided into two separate areas being separated by an insulating strip with a predetermined shape, and a sliding contactor riding on the surface of said drum, said contactor being movable over the surface of said drum carried by an arm pivoted about a point fixed relative to the rotational axis of said drum, the improvement comprising swivel mounting means for said contactor to maintain even contact pressure over the entire contacting surface of the contactor, a bracket attached to said arm, and spring means for applying contact pressure to said contactor, said arm, said bracket and said swivel mounting means all supporting said contactor for movement over the surface of said drum parallel to the axis of the drum.

3. In combination a contact drum, means for continuously rotating said drum about its longitudinal axis, a sliding contactor spring biased into contact with the surface of said drum, swivel mounting means for said contactor to maintain even pressure over the whole contacting surface of the contactor, means for positioning said sliding contactor to cause it to move over the surface of the drum parallel to the longitudinal axis of the drum, and insulation means on the surface of said drum for separating said surface into two se tions insulated from one another, said insulation means being of a configuration su h that said contactor will complete a piurality of cycles of contacting one of said drum sections and then the other.

In combination a contact drum, means for continuously rotating said drum about its longitudinal axis, a sliding contactor spring biased into contact with the surface of said drum, an arm supporting said sliding contactor, said having a bearing for pivoting the arm about an axis at right angles to the longitudinal axis of said drum, a swivel mounting on said arm for said sliding contactor to maintain even contact between the full Width of the contactor and the drum, said arm being positioned relative to said drum so that said contactor slides in a path parallel to the longitudinal axis of the drum, and an insulation strip on the surface of said drum for dividing the surface of the drum into separate areas, said strip having a configuration such that a plurality of cycles are completed in one revolution of the drum when the contactor is over the insulation strip.

5. In combination a contact drum, means for continuously rotating said drum ah tud nal axis, a sliding contacto into contact with the surface o: c-0111, an arm supporting said sliding con ctor, said arm having a bearing for pivoting the arm about an axis at right angles to the longitudinal of drum, cross arin swiveled near the end of said first mentioned arm, a s 1 said cross arm for said sliding contact tain even contact between the full th of the contactor and the drum, a b cket on said first for support g the spring that biases said sl contactor i to co act with the drum, said first mentioned a n be positioned relative to said drum so that said slides in a path parallel to the longitudinal axis of the drum, and a zig-zag shaped insulation strip having parallel sides, said strip dividing the surface of t e drum into separate areas for alternate contacting by said contactor, said zig-zag strip loeing configured to produce tvvo complete cycles of alternate contacting in one revolution of the drum.

biased No references cited. 

